In the last several decades, the rapid development and commercialization of wireless technology has fundamentally changed society. From the development of smart devices to driver-less transportation, this wireless revolution has changed how one interacts with their environment. With an ever growing set of devices that utilize wireless communication, there is a need for low-cost electromagnetic (EM) radiation sensors.
Conventional millimeter (mm) and sub mm wavelength detection technology (e.g. very small band gap semiconductors and/or cryogenically cooled detectors) are too expensive to be commercially developed for the standard consumer.
In most methods of detecting optical EM radiation, the photoconductive response of a semi-conductor is often used, e.g., silicon based photo-receivers. While useful in the optical regime, due to the low photon energy of mid to far-infrared radiation, other materials must be sought out. For mid-infrared detection (λ=3-8 μm) mercury cadmium telluride (MCT) detectors have become widely used, however their sensitivity dramatically decreases as one increases the EM wavelength. In addition, both single and multi-channel MCT detectors can be very expensive (greater and $2,000 and $50,000, respectively) and require complex control circuitry for bias and readout.
For radiation wavelengths that exceed 10 μm, cryogenically cooled detectors such as liquid helium cooled silicon bolometers are used. While efficient, the size (approximately the size of a toaster oven) and cost (greater than $30,000) of the single channel bolometers makes them impractical for many field and/or clinical applications. In addition, making these devices into multi-dimensional arrays for imaging is very challenging and cost-prohibitive.
Recent alternatives to direct detection methods include optical based THz spectroscopy methods. In these method free space electro-optic sampling (FSEOS) or optical gating of a photoconductive switches are typically used. FSEOS converts the temporal signature of THz radiation to the visible portion of the electromagnetic spectrum, thereby allowing optical detection technologies to measure the amplitude and phase of coherent THz radiation. Optical gating of photoconductive switches utilizes the transient electric field of the THz radiation to drive a current in optically excited semi-conductor. However, as the time-integrated electric field of the EM wave is still zero, this device requires the use of an ultrafast optical source to temporally gate the signal to determine the magnitude and direction the propagating wave.
There is a need for EM sensors that are smaller and more cost-effective than conventional sensors such as those described above. The invention addresses these needs among others.